1. Field of the Invention
The present invention relates to a feed additive which is highly flowable and cakes less as well as to a process for producing the same. The feed additive of the invention mainly contains amino acids and is useful as an additive for animal feed, especially, for feed for pigs.
2. Discussion of the Background
Amino acids are well known as feed additives and can be obtained in highly pure form. For example, crystals of L-lysine (L-Lys) hydrochloride (HCl) can be obtained by crystallizing a solution of L-Lys HCl, separating crystals having a purity of not less than 99% and then drying them. However, it is not necessary to use L-Lys of such high purity in a feed additive.
Amino acid solids can also be formed by directly drying a solution of an amino acid with a purity of as low as from 30 to 60% based on dry solid. However, a feed additive containing such amino acid solids has extremely poor handleability due to its hygroscopicity and caking tendency. Therefore, feed additives have generally been formulated from purified amino acids to obtain a product having good handleability.
On the other hand, since it is economically more desirable to use less pure amino acids in feed additives, a method of forming the feed additive by directly drying a fermentation broth containing amino acids has been attempted (Soviet Patent No. 480,397, French Patent No. 2,217,347, etc). Unfortunately, powders formed using such methods retain many impurities contained in the broth, resulting in a product which is extremely hygroscopic and which cakes easily. Additionally, such powders often form large lumps, making the product hard to handle.
In order to avoid caking due to hygroscopicity and to form a feed additive with good handleability, a method has been disclosed in which an additive is mixed with a fermentation broth, and then the mixture is dried. In French Patent No. 2,217,347, a dehydrating agent such as powdery silica, expanded perlite, bone meal, rice bran, calcium carbonate or fluorine-free phosphate is mixed with a fermentation broth and dried. However, when these additives were mixed in amounts identical to or greater than that of the amino acids in the fermentation broth, no physically stable solid composition was formed.
U.S. Pat. No. 4,327,118 describes a method of forming a solid composition by drying a mixture of (1) an inorganic additive such as lime and carbon dioxide, or carbon dioxide combined with lime and precipitated magnesium carbonate or precipitated magnesium carbonate and (2) a condensed L-lysine fermentation broth. The content of L-lysine in the solid composition formed by the method, however, is from about 10 to 35%. This amount of L-lysine as an effective ingredient in a feed additive is not practically useful.
U.S. Pat. No. 5,431,933 discloses a method for obtaining granules with good handleability directly from a fermentation broths by first separating a part of the biomass from the fermentation broth and subsequently drying, for example by spray drying, the remaining fermentation broth.
Japanese Laid-Open Patent Publication No. 06-296460 (also EP 615693) discloses a method for preparing a granular product which is "only slightly" hygroscopic and sticky, by directly spray-drying a fermentation broth. Neither the caking property nor the agglomerability of the granular product after storage is disclosed.
U.S. Pat. No. 5,133,976 discloses a method for producing a stable dried product having reduced hygroscopicity by condensing and drying a fermentation broth of L-lysine which is obtained under special fermentation conditions. However, since it is necessary to ferment under specific conditions, the operation is complicated and not practical.